Known as sakadachikoma in Japanese, or "headstand spinning tops" - these wooden tops reverse as you spin them. The headstand koma come in a set of 10 or 100. A set of 10 of these plain tops is USD 13.99, and 100 is USD 150.
"There's something kind of addictive about spinning these and then watching them immediately go the other way. Love them!" - Greg (Melbourne, Australia).